This calculator performs the heat balance between the total heat absorbed in a radiant box, including the radiation to the shield tubes, and the exit temperature, Tg(bridgewall) that will support that heat transfer. Additionally, the calculator computes the balance between the burner release and the heat exiting the radiant section. Since, we are not performing convection heat transfer in this excercise, the convection heat transfer per ft2 of the shield tubes, must be input. The heat in the exit flue gas is from the radiant section and does not account for the convection heat transfer in the shield.
| qr = Radiant heat transfer, Btu/hr | qc = Convection heat transfer, Btu/hr | |
| s = Stefan-Boltzman constant, 0.173E-8 Btu/ft2-hr-R4 | a = Relative effectiveness factor of the tube bank | |
| Acp = Cold plane area of the tube bank, ft2 | F = Exchange factor | Tg = Effective gas temperature in firebox, °R | Tw = Average tube wall temperature, °R |
| hc = Film heat transfer coefficient, Btu/hr-ft2- °R | At = Total outside area of the tubes, ft2 | |
For this calculator, the combustion air is at 60 °F, so the qair factor drops out of the equation. The fuel is gas, so there is no atomization and we are assuming it to be at 60 °F, so the qother factor also drops out of the left hand side. The equation can now be stated as,
| qrls = Burner release, Btu/hr |
| qS = Radiation heat transfer in shield section, Btu/hr |
| qloss = Setting loss as % of Release, % |
| qout = Heat leaving radiant section, Btu/hr |